As compared with non-tabular AgX grains, use of tabular AgX emulsion grains in photographic light-sensitive materials reduces the ratio of incident light's passing through the light-sensitive layer without being utilized, to thereby increase efficiency of light absorption (trapped light), and such use also brings about improvements in image quality in terms of covering power, sharpness and graininess (granularity), development progress, spectral sensitization characteristics, and the like. Tabular grains having twinning planes parallel to each other and {111} faces as main planes have therefore been used frequently. While a {111} face is a face generally made up mostly of halide ions (hereinafter also referred to as X.sup.-), a {100} face is a face made up of Ag.sup.+ and X.sup.- alternating with each other, and it provides superior photographic properties. Therefore, interest has recently turned to tabular grains whose main planes are {100} faces. For the details of conventional {100} tabular grains, reference can be made to JP-A-51-88017 ("JP-A" means unexamined published Japanese patent application), JP-B-64-8323 ("JP-B" means examined Japanese patent publication), JP-A-5-281640, 5-313273, 6-59360, and 6-324446, EP-A-0 534 395 (Al), and U.S. Pat. Nos. 5,292,632, 5,314,798, and 5,264,337. The present invention is to provide an improved {100} tabular grain emulsion as compared with the conventional {100} tabular grain emulsion. While {100} tabular grains owe their tabular form to crystal defects that enable preferential growth in the edge direction, the shape characteristics and photographic characteristics of tabular grains largely vary depending on the method of crystal defect formation. These characteristics also largely vary depending on the method of grain growth. Hence, improvements in methods of defect formation and grain growth have been attracting attention.
EP-A-0 534 395 (Al) describes a method of forming tabular grains in the presence of an adsorbent that accelerates the formation of a {100} face. However, the technique disclosed yields unsatisfactory results in terms of grain shape and photographic properties.
Further, conventional {100} tabular grains are also practically unsatisfactory in terms of suppression of dependence on a processing solution pH and preservability of a latent image.